The control of active and reactive power at the wind farm level in response to frequency and voltage or power factor controls is a well known and widely studied topic.
On the one hand, with the aim of modifying the voltage in the connection point, the central control system emits the necessary reactive power instructions for each wind turbine, while a possible individual control of each wind turbine, like that described in patent application EP1512869A1, is responsible for making sure that the limits permitted in each of them are not exceeded.
On the other hand, in order to collaborate in limiting the frequency of the electrical network to within a certain range, a control is carried out over the active power generated, from which derive the individual instructions for each wind turbine. An example of this type of control is that of patent application EP1467463A1.
The reactive power control has typically been carried out based on the desired power factor and, taking into account the active power generated, calculating the necessary global reactive power and sending the power factor instructions to each wind turbine.
As cited in U.S. Pat. No. 6,924,565, the drawback of such control lies in the fact that the total capacity of each wind turbine fails to be exploited. That patent proposes alternative methods for the generation of reactive power having the aim of exploiting the entire said capacity based on the level of active power generated at each moment.